The indexdbshim erros should not be affecting anything. It is related to the blackbox logging code that stores telemetry data for later download. I will take a look as clearly it is trying to reach out on the net to download something which won't work when the ROV does not have internet access!
We have disabled the TRIM feature in the current release. You can do the same by going through the /src/plugins/rovpilot/public/js/rovpilot.js file and commenting out the trim keyboard mappings manually.
For the vertical thruster, there is a mtarg and motors telemetry item that would be useful in debugging. mtrag is the target value for the thrusters and motor is the actual value that has been sent so far. The middle value is the vertical thruster value. 1500 is neutral.
If the mtarg is neutral (1500,1500,1500) and you still see the motor spinning, then we are dealing with a calibration of the ESC issue.
If you do see mtarg changing, when we have to track down what is causing the value to change when pressing a button. If you are having issues with the trim functions, that could be to blame.